Charles e



(No Model.)

C. E. CARPENTER.

REEOSTAT PLATE. No. 492,757. Patented Peb. 28, 1893.

WITNESSES: INVENTOR M, C/ww UM ATTORNEY UNITED STATES PATENT OFFICE.

CHARLES E. CARPENTER, OF BRIDGEPORT, CONNECTICUT, ASSIGNOR TO THE CARPENTER ENAMEL RI-IEOSTAT COMPANY, OF SAME PLACE.

RH EOSTAT-PLATE.

SPECIFICATION forming part of Letters Patent No. 492,757, dated February 28, 1893.

Application filed October 27, 1892. Serial No. 450,122. (No model.)

T a/ZZ whom it may concern:

Be it known that I, CHARLES E. CARPENTER, a resident of the city of Bridgeport, county of Fairfield, and State of Connecticut, have invented acertain new and useful Improvement in Resistance or Rheostat Plates, of which the following is a specification.

My invention relates to an improvement in resistance plates, or rheostats, for use with io dynamo machines and other electrical apparatus, and consists of the novel construction hereinafter more fully described and claimed.

The class of plates to which my present invention relates is that in which the resistance or rheostat consists of a Wire embedded in enamel which is baked or fused on to a base plate of metal, substantially in the manner set forth and described in my Letters Patent No. 447,023, of February 24, 1891.

zo One of the objects of the present improvement is to construct the base plate of varying thickness in cross sections so that during the process of firing in the furnace the base plate is heated uniforinlythroughoutandtheenamel 2 5 thereby evenly baked on to its surface.

My invention is illustrated by the accompanying drawings in Whichz Figure 1 is a cross-section of one form of my improved rheostat or resistance plate.

3o Fig. 2 a similar View of onemoditication thereof, and Fig.3 a similar view of another modification.

E represents the enamel, or its equivalent, whichserves to secure the resistance to, but

insulate it from the surface plate, and protects it from chemical action.

R is the resistance Wire embedded in said insulating material, A the supporting surface plate, and B the flange, which serves to preio vent the flowing 0E of the enamel, as above described, and also serves to protect the edges of the enamel from mechanical injury.

In Fig. l the rheostat plate, embodying my invention, is thickened at the edges. In this iigure is shown the manner in which the enamel is deposited Where no flange is provided at the edges. Fig. 2 is also a section of a plate, embodying my invention, but said plate is provided With a flange B, around its 5o edges, for the purpose hereinafterdescribed. Fig. 3 shows a supporting surface plate in rapid heating of the edges.

which the edges of the plate are not increased in thickness, except the flange for confining the enamel as hereinafter more fully described.

Heretofore in the preparation of resistance plates of the kind described it has been a difficult matter to bake or fuse the enamel evenly and of uniform depth upon the surface of the base plate, because certain portions, notably 6o the edges orsides of the plate would heat more rapidly, and in consequence the enamel or insulation thereon, would be overheated before the inner portion or center of the plate Was sufficiently heated to properly fuse or bake the enamel thereon. To obviate this difficulty,the edges or outside portions of the plate A are made thicker or of greater cross section, than the inner portion as shown in Fig. l, so as to provide a greater bulk of the 7o metal for counter-acting the, otherwise, more Vith this construction it will be seen, that the plate will be more uniformly heated throughout at the same time, and consequently the enamel will fuse alike throughout all portions of the surface.

Another object of my invention is to so construct the base plate A that the enamel Will be of uniform thickness throughout. In the 8o application of enamel to the surface plate, the enamel While Wet, as in what is known as the wash-process, will not be deposited at the edges of tne plate so thick as at other portions of the surface because it drains off, and sufficient enamel is not left at the edges of the plate to insulate the wires properly and otherwise protect them. For this reason I provide a rim B at the edges of the plate A, which prevents the enamel from flowing off, 9o and tends to con line it to the proper place, resulting in a more perfect insulation and better protection to the Wires. This rim also serves to protect the enamel at the edges of the plate from mechanical injury.

I claim-- l. A resistance, or rheostat, consisting of a base plate having thickened edges, a coating of enamel baked on the surface thereof, and resistance coils embeddedin said enamel, subrco stantially as and for the purpose described.

2. In a resistance, or rheostat, a support plate having thickened edges and a flange around said edges, in combination with a coating of enamel, upon the surface of said support plate, substantially as and for the purpose described.

3. In a rlieostat in which the resistance is embedded in enamel, or its equivalent, a supporting plate which is thicker at the edges than at the center, substantially as described.

4. A resistance or rheostat having a base plate provided with a rim 0r ange at the edges of the plate and an insulating material 

